A cylinder-head gasket is compressed between the cylinder head and engine block of an internal-combustion engine and is formed with cylinder or gas-passage holes, with bolt or stud holes, and with liquid-passage holes. The purpose of the head gasket is to maintain a predetermined spacing between the cylinder head and the engine block and to prevent leakage between the various passages extending through the gasket and from these holes to the exterior. Obviously the head gasket is subjected to considerable pressure, heat, and even chemical action.
It is therefore standard practice to form such a head gasket of asbestos or metal-clad asbestos. The standard procedure on assembling a cylinder head is to torque it down with the required force during assembly, and thereafter at regular intervals for a short run-in period to torque it down again, ensuring that constant pressure is maintained as the gasket flattens out and conforms to the surfaces it is sandwiched between.
Such an asbestos cylinder-head gasket is therefore disadvantageous in several respects. The use of asbestos itself demands expensive manufacturing techniques in order to protect those involved in the manufacture from this dangerous material. The retorquing of the cylinder head is also an onerous operation which, if forgotten, can result in serious damage to the engine.
Accordingly it has been suggested to use a metallic head gasket having elastomeric seal rings around the liquid-passage holes through which coolant water normally passes. Different metallic seal rings are provided around the edges of the gas-passage holes constituting the ends of the engine cylinders. Such a gasket need not be retorqued, but fabrication costs for it are quite high.
In French patent No. 79 08917 a head gasket is described which is made of a synthetic resin or of rubber and which incorporates solid spacers which ensure proper spacing of the cylinder head and block. Such a head gasket, however, has been found to be extremely prone to failure in engines operating at high temperature, as many of the modern high-RPM fuel-efficient ones do. At the high temperatures of around 130.degree. C.-150.degree. C. this gasket softens so much that it easily blows out.
Thus a procedure has been developed of incorporating a metal skeleton in such a gasket. Appropriate portions of the gasket are made of metal, and metallic rings are incorporated in it around the various holes. Although such a gasket can function adequately, its fabrication costs are quite high, particularly because of the considerable material losses inherent in its production from a flat continuous metal blank and the difficulty of positioning the various metallic elements in the mold for the gasket.